Most of the eastern half of the country has between 750 and 1000 millimetres (mm) of rainfall in the year. Rainfall in the west generally averages between 1000 and 1250 mm. In many mountainous districts rainfall exceeds 2000mm per year. The wettest months, in almost all areas are December and January. April is the driest month generally across the country. However, in many southern parts, June is the driest. Hail and snow contribute relatively little to the precipitation measured.

Measuring Rainfall

Rainfall amounts are collected by a standard gauge, consisting of
a funnel and a container. The 15 Meteorological Service stations around
the country measure these rainfall amounts every hour. However,
most of the 750 or so rainfall stations around the country read their
gauges once a day. A few gauges in remote mountain locations are only
visited once a month.

Rainfall Records

Driest
year 1887-only 356.6mm of rain recorded at Glasnevin Dublin

Longest absolute
drought Limerick 3rd April to 10th May 1938

Greatest monthly total 790.0mm
Cummeragh Mtns October 1996

Greatest annual total 3964.9mm Ballaghbeena
Gap 1960

Greatest hourly total 97mm Orra Beg, Antrim, August 1980

Greatest daily
total 243.5mm Cloone Lake Co. Kerry 18 September 1993

How Often Does it Rain?

The general impression is that it rains quite a lot of the time in
Ireland but in fact two out of three hourly observations will not report
any measurable rainfall. The average number of wet days (days with
more than 1mm of rain) ranges from about 150 days a year along the
east and south-east coasts, to about 225 days a year in parts of the
west.

How Heavy is the Rain?

Unlike the rain in many other countries, especially in the tropics, average
hourly rainfall amounts in Ireland are quite low, ranging from 1 to
2mm. Short-term rates can of course be much higher: for example, an
hourly total of 10mm is not uncommon and totals of 15 to 20mm in an
hour may be expected to occur once in 5 years. Hourly totals exceeding
25mm are rare in this country and when they do occur they are usually
associated with heavy thunderstorms.